Method and system for building painted three-dimensional objects

ABSTRACT

Methods of printing a three-dimensional object, layer by layer are provided. Layers are formed by printing a bulk region with a white building material; inkjet printing a circumferential region surrounding the bulk region that is part of an apparent colored surface of the three-dimensional object, the circumferential region includes colored voxels formed by depositing a transparent building material and one or more color additive materials and inkjet printing a transparent layer around the circumferential region.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/696,878, filed Apr. 27, 2015, to be issued asU.S. Pat. No. 9,738,033, which is a continuation application of U.S.patent application Ser. No. 13/195,667, filed Aug. 1, 2011, U.S. Pat.No. 9,020,627, which in turn is a continuation application of U.S.patent application Ser. No. 12/364,595, filed Feb. 3, 2009, now U.S.Pat. No. 7,991,498 all of which are incorporated herein in theirentirety.

BACKGROUND

In three-dimensional printing, the object is formed by selectivelydepositing material from a deposition device, such as an inkjet printhead in successive layers based on cross sections of the object.Although, for most applications the final product can be uni color, insome cases, a painted three-dimensional object is desired.

There have been some attempts to disclose methods for formation ofcolored objects, for example by using a plurality of printing heads thateject building materials of different colors throughout the entirelayer. These methods cannot produce, however, a three-dimensional objectwith a high-quality painted surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 is a flowchart diagram of a method for forming g a threedimensional colored object according to embodiments of the invention;

FIG. 2 is graphical representations of an exemplary bitmap of a layer ofthe 3D object according to embodiments of the invention; and

FIG. 3 is a schematic illustration of an exemplary printing systemaccording to embodiments of the invention.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

The processes presented herein are not inherently related to anyparticular computer or other apparatus. Various general-purpose systemsmay be used with programs in accordance with the teachings herein, or itmay prove convenient to construct a more specialized apparatus toperform embodiments of a method according to embodiments of the presentinvention. Embodiments of structures for a variety of these systemsappear from the description herein. In addition, embodiments of thepresent invention are not described with reference to any particularprogramming language. It will be appreciated that a variety ofprogramming languages may be used to implement the teachings of theinvention as described herein.

Although embodiments of the invention are not limited in this regard,discussions utilizing terms such as, for example, “processing,”“computing,” “calculating,” “determining,” “establishing”, “analyzing”,“checking”, or the like, may refer to operation(s) and/or process(es) ofa computer, a computing platform, a computing system, or otherelectronic computing device which may be included in a printing machine,that may manipulate and/or transform data represented as physical (e.g.,electronic) quantities within the computer's registers and/or memoriesinto other data similarly represented as physical quantities within thecomputer's registers and/or memories or other information storage mediumthat may store instructions to perform operations and/or processes bythe printing machine or elements, parts, modules or units of a printingmachine.

Although embodiments of the invention are not limited in this regard,the terms “layer” and “object layer” as used herein may be usedthroughout the specification and claims to describe any lamina or filmthat may represent a cross-section or slice in an X-Y plane of athree-dimensional object. A layer may be formed and adhered topreviously formed and adhered layers in a “layer by layer” fashion tocreate, build up or form in the Z direction a three-dimensional object.

Embodiments of the present invention are directed to a method ofselectively depositing materials, layer by layer, to form a painted orcolored three-dimensional (3D) object. The 3D colored object may beformed by selectively dispensing colored materials on at least a portionof the outer circumference of at least some of the layers. The width ofthe circumference or outline of a layer may include a few pixels and maybe, for example, between 0.1 and 1 mm.

According to some embodiments, a white barrier outline may be formedadjacent to the colored outline of the layer using white buildingmaterial and the building material used for the bulk of the 3D objectmay be transparent, white or colored, as desired. The white outline maybe used as a white background to the apparent colored surface to ensureperception of bright colors and a large color gamut. It may enable usingcolorant types similar to those used for 2D white page printing.Further, the color calculations may be based on 2D color theoryutilizing process color systems such as CMY, CMYK or CMYOGK. As known toa person skilled in the art, C stands for cyan, M for magenta, Y foryellow, O for orange, G for green and K for black.

According to embodiments of the invention, the method may includegenerating the image data by dividing the apparent surface of the 3Dobject into 3D color cells where each colored cell is defined by atangential area with respect to the apparent surface and a depthdimension directing toward the inner region of the object. According toembodiments of the invention, the size of each 3D color cell may bedetermined according to the desired color spatial resolution and thedesired color shade resolution in the surface area associated with the3D color cell.

The method may further include generating color patterns for the 3Dcolor cell according to the desired color shade of the cell, namelydetermining within the cell the desired basic color for each buildingvoxel (volume pixel). The color pattern of the 3D color cells andadditional data related, for example, to the shape of the object may beused as input data for generating the two-dimensional (2D) image datafor each cross sectional layer of the object. In particular, based onthe color patterns of the 3D color cells, the outline color datarepresenting the outer circumference of each layer may be generated. The2D image data of the layers may be used to selectively deposit materialsof different colors based on the 2D image data to produce the 3D coloredobject.

As should be understood to a person skilled in the art, based on colormanagement theory, the visual color at a point on the surface is“determined” by the color at that point and the colors of adjacentpoints on the surface and near the surface within the object. Therefore,each point may be affected by its adjacent points on the surface andwithin the object. It should be understood that these points aredistributed across a plurality of printable layers that representdifferent parallel cross sections of the object.

The color pattern for the apparent surface of the 3D object may bedetermined using any known process color system. For example, athree-color system (CMY) that uses three basic colors, cyan (C), yellow(Y), and magenta (M) where black is provided by a substantially evenamount of cyan, yellow or magenta or a four-color system CMYK that usesalso black (K) color. According to embodiments of the invention, anadditional white color (W) may be required to reflect the colorantswhich are not transmitted by the process colors and to be able to use alarge number of different colors and shades.

In two-dimensional (2D) printing, the range of colors may also beincrease by half toning. Half toning permits one to print using lessthan full saturation of the primary or basic colors (CMY). Using thisprocess, small dots of each primary color may be printed in a patternthat may be small enough that the human eye may only perceive a singlecolor. For example, in order to create the color green, one may create ahalftone mix of cyan and yellow. Half toning is usually described interms of gray levels. In 2D printing, the number of “gray levels” foreach colorant (such as C,M,Y) is

N _(gray) =N _(x) *N _(y),

where N_(x) is the number of pixels in the 2D color cell in X directionand N_(y) is the number of pixels in the 2D color cell in the Ydirection.

Accordingly, the number the number of different colors in 2D printing is

N_(printing)=N_(gray) ³ for the 3-color system.

Similarly, in three-dimensional (3D) printing, the number of gray levelsfor each colorant is equal to the number of voxels in the 3D color cellthat is used to create the local color. For example, in the case ofpainting the outer surface of the object, the number of gray levels is

N _(gray) =N _(x) *N _(y) *N _(Z),

where N_(x), N_(y) and N_(z) are the number of pixels in the color cellin the X, Y and Z directions respectively.

In 3D printing, the 3D color cell may include both colored and uncoloredvoxels. The colored voxel may be formed by depositing both a transparentbuilding material and a color additive onto the same point or bydepositing a colored building material. The uncolored voxels may beformed by depositing white building material. The number of possibledifferent colors, N_(printing (3D)) may be different from number ofpossible different colors, N_(printing) in 2D printing, when usingcolored building materials where the volume of the droplets of thedifferent colored building materials is substantially the same. This isdue to the fact that once a voxel is filled with a colored buildingmaterial, it cannot accept another colored building material color. Thenumber of color combinations in this case for a 4-color system is

N _(printing(3D)) =N _(gray)!/((N _(gray)−4)!*4!) and

N _(printing(3D)) =N _(gray)!/((N _(gray) −n)!*n!), for the general caseof the n-color system.

When the color material is deposited in a form of an additive where thedroplet volume of the additive is much smaller than the droplet volumeof the building material, more than one color additive may be added toeach voxel. Therefore, in this case, the number of color combinations is

N _(printing(3D)) =N _(gray) ^(B) for an n-color system, where nrepresents the number of color materials.

It should be mentioned that the resolution of the printing heads andbitmaps associated with the color additives may be different than theresolution of the printing head and bitmaps associated with buildingmaterial. This is because the size of the colored material droplets doesnot necessarily have to be equal to the building material droplets.Using smaller droplets for the additive may increase the number of graylevels. For example, if the color resolution is twice the buildingmaterial resolution in both the X and Y directions, the number of graylevels for each color, N_(gray) would be 4 times larger than the numberof gray levels of a color that resolution that is identical to thebuilding material resolution. According to exemplary embodiments of thepresent invention, the volume of each droplet of the color additive maybe 1/5 of the volume of each building material droplet.

Reference is now made to FIG. 1, which is flowchart diagram of a methodfor generating a color pattern for the apparent surface of a 3D objectand 2D image data for printing the 3D painted object according toembodiments of the invention. The method of assigning color to theapparent surface of the object may include dividing the apparent surfaceof the object into small patches where each patch defines a face of a 3Dcolor cell (box 100). According to embodiments of the invention, eachpatch lies in a plane perpendicular to the normal of the surface at arespective point and has a tangential size which is determined by thedesired spatial resolution of the color. The depth or thicknessdimension of the 3D color cell may be determined by the number of graylevels that is desired for the color cell, namely, the color shaderesolution.

Next, the process may include calculating the number of voxels in eachcolor cell that should receive each of the basic colors (box 200).Accordingly, the process may include determining, for each color cell,the number of basic colors that should be assigned to the cells andwhich basic colors should be assigned to that cell and then calculatingthe number of voxels in the cell that should receive the assigned basiccolors. The assigned basic colors may be scattered evenly within thecolor cell among the voxels associated with the particular cell. Whenthe basic colors are deposited as additives to a transparent buildingmaterial, more than one basic color may be deposited onto the samevoxel. In such case, each basic color may be added to any number ofvoxels that is equal or smaller than the total number of voxels (N) inthe 3D cell. When the basic colors are deposited as building materials,each voxel can accept only one color.

When the basic colors are deposited as additives to the buildingmaterial, the calculation of the color pattern of the color cell orcolor separation is similar to the calculation for 2D printing. Itshould be understood to a person skilled in the art that although theapparent surface of the object may not be flat, the area of the surfacethat is associated with a single color cell is small enough to beregarded as an area on a plane perpendicular to the normal to thesurface at a point on the surface. Further, it should be understood to aperson skilled in the art that the calculation of a color pattern of the3D cell may be performed similarly to the calculation of a 2D colorpattern since for a subtractive color system, such as YMCK, the colorappearance of an area would be the same for a 2D cell or a 3D cellhaving the same mixture of basic colors and there would be no differenceif the colored voxels are behind each other or near each other.

The calculation of color separation may be modified when the basiccolors are a-priori inserted into the building materials to form coloredbuilding materials. As discussed, in such case, no more than one colormay be assigned to a particular voxel. Accordingly, if the calculationof the color pattern results in the need for more voxels that may existin the 3D cell, the number of voxels in the call may be increased byincreasing the depth dimension of the cell. Alternatively, the number ofcolor voxels for each separation may be proportionally decreased so thatthe sum of color voxels would not exceed the number of voxels in the 3Dcell.

Next, the process may include assigning the colors to voxels in the 3Dcolor cells by arranging the colors within the cell. According toembodiments of the invention, the colored voxels are chosen to be closeto the apparent surface, if possible (box 300). The outcome of thisprocess is the color pattern for the 3D cell where each voxel is eithera colored voxel for which one or more basic colors are assigned to oruncolored voxel on which a white building material would be deposited.Then, using the color patterns, the two-dimensional (2D) image data foreach cross sectional layer of the object may be generated (box 400).According to embodiments of the invention, the image data may include awhite barrier outline having a width of several voxels located adjacentto the colored outline of the layer. The white building material may bedeposited in each 2D layer to form a white barrier in the final productplaced in between the apparent painted surface and the interior of theobject that may be transparent. As discussed, the color calculation andcolorant type may become similar to those used in the field of 2Dprinting on a white substrate.

According to some embodiments, the image data may include a transparentlayer as the outer layer. The transparent layer may serve as aprotective layer to protect the painted surface from deterioration andcolor modification over time. The transparent layer may increase theglossiness of the color and/or add hardness to the surface.

According to embodiments of the invention, the number of gray level foreach base color, namely the desired color shade resolution may beselected independently of the desired color spatial resolution that isdetermined by the size of the tangential area of the cell. This is incontrast to 2D printing where the color spatial resolution and the colorshade resolution are dependent of each other. As known to a personskilled in the art, there is a tradeoff between the size of the 2D celland the number of gray levels for each basic color. Accordingly, when ahigh spatial resolution is desired, the size of the 2D color cell ischosen to be small and therefore the number of pixels is reduced, whichin turn reduces the number of possible gray levels. According toembodiments of the invention, the number of possible gray levels in a 3Dcolor cell may be adjusted by changing the depth dimension of the cellwithout changing the tangential area of the cell. For example, for givensize of tangential area, the number of voxels in the cell may beincreased by increasing the depth dimension of the cell.

According to embodiments of the invention, a user or a software modulemay determine a desired spatial resolution and a desired color shaderesolution for a basic color. color shade resolution). The desiredspatial resolution may determine the size of the tangential area Δs forall the color cells. Based on the desired color shade resolution, thenumber of gray levels per color may be determined. The depth dimension(d) of the 3D cell may be determined as follows:

D=v*N/Δs,   [eq. 1]

Where v is the volume of a voxel and N is the number of voxels in the 3Dcell. When the basic colors are additives to the building material, Nmay be regarded as equal to the desired number of gray levels per color.

According to embodiments of the invention, the size of the tangentialarea Δs may vary according to the content of the painted surface. Forexample, if the required color varies strongly between a first area onthe surface and a second area, the software may determine, in order toachieve a better print quality, that the tangential area for color cellsin the first area may have smaller size than the tangential area forcolor cells in the second area. Optionally, in order to preserve a fixednumber of voxels, the depth dimension of the cell may be variedaccording to Eq. 1. Alternatively, both the size of the tangential areaΔs and the number of voxel in the cell may be determined locally basedon the content of the painted surface.

Reference is made to FIG. 2, which is a schematic representation of alayer bitmap of a three-dimensional object according to embodiments ofthe invention. In some embodiments, layer bitmap 10 may comprisebuilding material pixels 12, namely pixels representing a command todeposit non-colored building material, white pixels 14 representing thewhite barrier, and colored pixels 16. As illustrated, colored pixels 16are only located on the outer circumference of layer bitmap 10. Asillustrated, the width of the white barrier is 4 pixels for the entirecircumference of the barrier. It should be understood that embodimentsof the invention are not limited in this respect and other width may belikewise applicable. Colored pixels 16 may be intended to accept one ormore basic colors. The color white may be used on the apparent outersurface in cases where any of the other colors are not used. The reasonfor this is so that the outer surface of the three-dimensional object iskept smooth.

The remainder of layer bitmap 10 may comprise building material pixels12. According to some embodiment, the building material is transparent.In another embodiment, the building material may be white material. Inthis case, there is no need for white pixels 14, as the white buildingmaterial may serve the same purpose as white pixels 14. It should,however, be understood to a person skilled in the art that embodimentsof the invention are not limited in this respect and that the buildingmaterials may be tinted with any other color.

Reference is made to FIG. 3, which is an illustration of a depositingsystem for producing painted three-dimensional objects according toembodiments of the invention. A deposition system, such as, an inkjetprinting system 30 may include a fabrication platform or tray 32, aprinting head 34 that is used to dispense building material and at leastone colored printing head 36 that is used to dispense colorants. Forexample, in the case where a 4-color system may be used, the system maycomprise four separate color printing heads 36. System 30 may furtherinclude a leveling device 38 and at least one curing unit 40. Printingheads 34 and 36 may be coupled to a moving frame 42 to enable theprinting heads to move above fabrication tray 32 in both X and Ydirections.

System 30 may further include a controller 44, such as a microprocessorto control the printing process. Such a controller may includecomponents such as, but not limited to, a plurality of centralprocessing units (CPU) or any other suitable multi-purpose or specificprocessors or controllers, a plurality of input units, a plurality ofoutput units, a plurality of memory units, and a plurality of storageunits. Such system may additionally include other suitable hardwarecomponents and/or software components. Controller 44 may instruct theprint heads to selectively deposit building materials and coloradditives based on image data generated according to embodiments of thepresent invention. Accordingly, controller 44 may includecomputer-storage medium having stored thereon instructions that may bedelivered to the printing heads for selectively printing layer by layer.

The material used in color printing heads 36 may or may not be the samematerial which is used for the building material. In general, thebuilding material may be a photopolymer with a high viscosity. Accordingto embodiments of the invention, the colored material may be an additiveto the building material made of a material that is not polymerizable.For example, the colorant may be based on a low viscosity material toenable the use of unheated printing heads. Since the quantity of coloredmaterial used in each layer is only a fraction of the total amount ofmaterial used in each layer, the storage tanks (not shown) used for thecolored material may be placed as close as possible to colored printingheads 36, while the storage tank (not shown) used for the buildingmaterial may placed in a stationary location and connected to printinghead 34 by pipe.

According to embodiments of the invention, the color additives may bedispensed before the building material, so that leveling apparatus 38may not reduce the amount of the colorant. In some embodiments, printinghead 34 may be placed between leveling apparatus 38 and color printingheads 36.

Although embodiments of the invention are not limited in this regard,the terms “plurality” and “a plurality” as used herein may include, forexample, “multiple” or “two or more”. The terms “plurality” or “aplurality” may be used throughout the specification to describe two ormore components, devices, elements, units, parameters, or the like. Forexample, “a plurality of printing heads” may include two or moreprinting heads.

Embodiments of the invention may include an article such as a computeror processor readable medium, or a computer or processor storage medium,such as for example a memory, a disk drive, or a USB flash memory,encoding, including or storing instructions, e.g., computer-executableinstructions, which when executed by a processor or controller, carryout methods disclosed herein.

Some embodiments of the present invention may be implemented in softwarefor execution by a processor-based system. For example, embodiments ofthe invention may be implemented in code and may be stored on a storagemedium having stored thereon instructions which can be used to program asystem to perform the instructions. The storage medium may include, butis not limited to, any type of disk including floppy disks, opticaldisks, compact disk read-only memories (CD-ROMs), rewritable compactdisk (CD-RW), and magneto-optical disks, semiconductor devices such asread-only memories (ROMs), random access memories (RAMs), such as adynamic RAM (DRAM), erasable programmable read-only memories (EPROMs),flash memories, electrically erasable programmable read-only memories(EEPROMs), magnetic or optical cards, or any type of media suitable forstoring electronic instructions, including programmable storage devices.

Such a system may include components such as, but not limited to, aplurality of central processing units (CPU) or any other suitablemulti-purpose or specific processors or controllers, a plurality ofinput units, a plurality of output units, a plurality of memory units,and a plurality of storage units. Such system may additionally includeother suitable hardware components and/or software components.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

1. A method of printing a three-dimensional object, layer by layer, themethod comprising: for a layer: printing a bulk region with a whitebuilding material; inkjet printing a circumferential region surroundingthe bulk region that is part of an apparent colored surface of thethree-dimensional object, the circumferential region includes coloredvoxels formed by depositing a transparent building material and one ormore color additive materials; and inkjet printing a transparent layeraround the circumferential region.
 2. The method of claim 1, wherein acolor additive material resolution is higher than a transparent buildingmaterial resolution.
 3. The method of claim 1, wherein at least one ofthe colored voxels includes at least two of the color additivematerials.
 4. The method of claim 1, wherein a droplet volume of thecolor additive materials is smaller than a droplet volume of thetransparent building material.
 5. The method of claim 1, wherein thebulk region of the layer further comprises the transparent buildingmaterial.
 6. A three-dimensional object printed in layers, whereinprinting a layer comprises: printing a bulk region with a white buildingmaterial; inkjet printing a circumferential region surrounding the bulkregion that is part of an apparent colored surface of thethree-dimensional object, the circumferential region includes coloredvoxels formed by depositing a transparent building material and one ormore color additive materials; and inkjet printing a transparent layeraround the circumferential region.
 7. The three-dimensional object ofclaim 6, wherein the bulk region of the layer is further printed withthe transparent building material.
 8. A method of printing athree-dimensional object, layer by layer, the method comprising: for alayer: printing a bulk region with a white building material; inkjetprinting a circumferential region surrounding the bulk region that ispart of an apparent colored surface of the three-dimensional object, thecircumferential region includes colored voxels formed by depositing oneor more colored building materials; and inkjet printing a layer oftransparent building material around the circumferential region.
 9. Themethod of claim 8, wherein the bulk region of the layer furthercomprises the transparent building material.
 10. The method of claim 8,wherein the circumferential region of the layer further comprises thewhite building material.
 11. The method of claim 8, wherein thecircumferential region of the layer further comprises the transparentbuilding material.
 12. A three-dimensional object printed in layers,wherein printing a layer comprises: printing a bulk region with a whitebuilding material; inkjet printing a circumferential region surroundingthe bulk region that is part of an apparent colored surface of thethree-dimensional object, the circumferential region includes coloredvoxels formed by depositing one or more colored building materials; andinkjet printing a layer of transparent material around thecircumferential region.
 13. The three-dimensional object of claim 12,wherein the bulk region of the layer is further printed with atransparent building material.